Couple quick questions if y'all don't mind.

[Dorado]

Well, I messed up. I tried to make my own archery target out of an old basketball and some expanding foam. I wasted two cans and it never worked. I'll skip it and save up for a better target.
Ya'll ever do that?

Main question.
I got me a section of wool that I'll be turning into a haversack/possibles bag for hunting and camping. I was wondering, the shoulder strap. Sides or back?
I can make it either flat and put the straps on the back or I can add sides to it and put the straps there. What have y'all experienced?
I'll be making the haversack probably around 11" wide by 10" tall with a button closure to keep it quiet.

[Roadkill]

Look at some black powder sites and look at some of those haversacks.  I am guessing, but your shoulder straps on the sides might be better if carrying weight.  Sewn on the back it may tend to lean away from the body, but again, I guess based on my issued map case from my time inthe service

[Rough Run]

Roadkill got it right, in my experience - straps on the side are stronger for carrying more weight.  I have carried a leather possibles bag for years, for all kinds of hunting.  The back is more streamlined, but the sides are stronger.

[Rough Run]

2 more points that I have found --
Narrow straps can cut into your shoulders, and tend to slide around more.  And, try 2 buttons at 1/3 increments, instead of 1 single button - you can leave one open, for a tall bottle or anything that doesn't fit perfectly, while keeping the other side closed for security of smaller items.

[Sam McMichael]

I have an Asbell haversack with straps on the ends and a military style bag with strap on the back side. I like the strap on the ends better. I would prefer a leather shoulder strap, though.

[Pat B]

I prefer straps on the sides. If you attach them angling towards the back a bit the bag will hang better. Also I like to add a bit of leather or piece of the bag material on the inside to help strengthen the attachment.

[Dorado]

That's about what I figured. My plan on them is simple. I'm going to cut the sides into a teardrop shape. The widest point would be no more that 4-5" tapering to 1" at the mouth. Single pocket. The body would be a single piece of wool about 10-11" wide. The lid I was thinking of cutting it triangularly but two buttons would be better and I do have a lot of OD green military buttons.
I want this large enough for me to fit my 14cm zebra pot, a day or two's worth of foodstuffs, map, notepad and pencil. Everything else as far as my hunting kit either goes in my quiver or on my belt, tomahawk, knife, canteen. I don't need much else. I usually stuff a wool blanket into the back of my belt. Oh, I have a WWII pistol belt and suspenders that I take hunting. I can fit a lot on that.

[Dorado]

Got my haversack nearly complete. What I ended up doing was cutting the main body 30"X12" and the sides are rectangular at 2"x11. I used some upholstery thread to sew it together and it came out alright for being my first sewing project in 15 years. I've got a 1" shoulder strap cut very long. Once I get the position and length where I want it I'll widen the shoulder part to spread the weight if I feel it's needed. I did load it with most of the gear I normally take minus food but I could still see me carrying that for hours on end as is.
I could not for the life of me figure out how to sew button holes so I took it to a seamstress and asked her to sew some on for me. I left some of my buttons with her so that she'd be able to fit it properly. I wasted a 4"X30" length of material trying to figure out buttonholes. I must have tried thirty times or better.